The development of semiconductor lasers in the past number of years has lead to a device of great reliability and usefulness. A useful reference for the properties of semiconductor lasers is Heterostructure Lasers by H. C. Casey, Jr., and M. B. Panish Academic Press, Inc., New York, 1978 Part A and B. Also useful as a background reference is U.S. Pat. No. 3,758,875 issued to Izuo Hayashi on Sept. 11, 1973 and U.S. Pat. No. 4,184,171 issued to Morton B. Panish on Jan. 15, 1980.
It has been found after extensive investigations that cleaved laser facets either with or without fabricated mirrors (such as evaporated metal mirrors or dielectric mirrors) yield the lowest thresholds and most reproducible device performance. A number of techniques are available for cleaving facets on semiconductor lasers including, for example, mechanically scribing marks on the semiconductor laser material and then cleaving the semiconductor material along the scribe marks. Another technique, called the micro-cleaving technique, is also used. Here, certain materials that form part of the supporting structure of the active part of the semiconductor laser is etched away and then the semiconducting material cleaved to produce the laser mirrors (See H. Blauvelt et al, Appl. Phys. Lett. 40 (4), 289 (1982) and O. Wade et al, Electronics Letters 18, No. 5, 189 (1982)).
It is highly desirable to have a procedure for accurately and reliably cleaving semiconductor laser crystals which is easily and rapidly applied in a manufacturing atmosphere. It is particularly desirable to be able to accomplish this on the entire array of semiconductor laser crystals on a semiconductor wafer. Ease and accuracy in producing scribe marks for cleaving as well as simultaneous application to a large array of laser structures (as on a semiconductor wafer) are of primary concern.
In addition, it is highly desirable for some applications to have the cavity length of semiconductor lasers very short. Shorter cavity lengths yield a longitudinal mode structure which is more spread out in frequency units (greater separation in modes in frequency units) so that single longitudinal mode operation is more easily achieved. More stable single mode operation is possible with shorter cavity length (See for example T. P. Lee et al, IEEE J. of Quantum Electronics, Vol. QE-18, No. 7, July 1982). Also, lower threshold currents are obtained with shorter cavity lengths down to cavity lengths in the range from 50-100 micrometers (see C. A. Burrus et al, Electronic Letters 17, 954-956 (1981)). Often, attempting to cleave laser crystals closer than the thickness of the semiconductor wafer proves very difficult, especially to obtain consistently reliable results with high yields.
For the above reasons, it is highly desirable to develop a fabrication procedure for making semiconductor lasers with cleaved mirrors with very short cavity lengths. Although the technique should be applicable to semiconductor lasers of any length, it should also give reliable results to cavity lengths less than 100 micrometers or even 50 micrometers or even 25 micrometers. Particularly desirable is a procedure which yields such laser structures with high reliability and high yield.